Guide: converting - multipass encoding

Multipass encoding is not so simple.  This is mainly because most video editing programs don't expect that an AVI codec COULD have multipass encoding.

IMHO, the best way is to first output to an uncompressed AVI with uncompressed PCM WAV audio, and then let VirtualDub do multipass encoding to AVI.

Firstly, have your project on whatever video editing program you are using all set out ready to output your short film (a masterpiece we hope!)  Make sure that the general settings are right.  That is:

• framerate = 25 fps (PAL) or 29.97 fps (NTSC)
• framesize = 640 x 480 (or 640 x XXX if you are making a widescreen production without letterboxing)
• audio sampling rate = 16-bit, stereo, 44.1 kHz

Now, on your video editor, change the AVI video codec to the below:

On the panel of codec choices, choose Uncompressed RBG

Click OK and you will have set up the video codec.

Now, you will have to set the audio codec settings.  The actually dialogue box will probably look different in your application but it should generally contain the same information.

Select "No compression / PCM"

And click OK.

Now, when you export your short film to AVI, it should be exported to uncompressed AVI and uncompressed PCM WAV audio.  This will ensure that there is no generational loss of quality.  The next step is to use VirtualDub.

Step 3: Multipass encoding with VirtualDub

Your first step is open up the AVI file you've created into VirtualDub.

File --> Open And open your file

Your next step is to set-up your audio codec / compression:

1. Audio --> set to "Source audio" 2. Audio --> set to "Full processing mode" 3. Audio --> click on "Compression"

Select Lame MP3 as the audio compression and 44.1 kHz, 128 kbit/s CBR, Stereo as the setting as below:

Select Lame MP3 --> and select 44.1 kHz, 128 kbit/s CBR, Stereo

Now, you will have to set up the video codec settings for the first pass.  Before, loading the settings, you should first calculate what the average video bitrate you will be using.  This is easily accomplished by the Bitrate Calculator application.

For example, if my film was 3 min and 40 sec in length and I was planning on using 128 kbit/s MP3 as the audio bitrate, then I simply put the values into the calculator and press "Calculate" to yield...

and the answer = 1397 kbit/s

... 1397 kbit/s.  Thus, if I wanted to stay within the 40 MB limit, my average bitrate for the video should be less than 1397 kbit/s.   If you want to upload a smaller file, then change the "filesize" to a smaller value and press calculate to determine your target bitrate.

And the settings for the first pass...

1. Video --> select "Full processing mode" 2. Video --> click on "Compression" On the panel of codec choices, choose DivX 5.0.5 --> then click on a button named "Configure" or "Settings"

You should set the DivX 5 codec settings to those below.  A slight slower bitrate is set compared to the calculated one so to ensure that the final filesize won't just be a little bit bitter than the maximum.

1. Bitrate control --> change the "Variable bitrate mode" to "Multipass, 1st pass" --> change the "Encoding bitrate" to the value calculated before (it's a good idea to use a slightly lower value as a buffer)

2. General parameters

3. Profiles Change to above to "Home Theatre" then put in the numbers relevant for your clip

Click OK and all the settings will be set!

Now, you should set to save the file to AVI, but rather than writing the file right away, add it to "job control"

File --> Save as AVI Set your file name --> check "Don't run this job now"

Then click on Save.  This will defer the actual job to "job control".  This is as you don't actually want VirtualDub to just encode the "first pass" (where no encoding actually takes place as such... rather the DivX 5 codec looks at the video file and writes down a log file containing encoding information).

Now, you want to change the settings in the DivX codec for the second pass...

1. Bitrate control --> change the "Variable bitrate mode" to "Multipass, nth pass" --> make sure that the encoding bitrate is the same as before --> the crucial bit: the update log file check box (read below)

The update log file check box is the crucial setting here:

• Unchecked: means that this is the LAST pass and the DivX codec will write the actual AVI file
• Checked: means that this isn't the LAST pass yet (e.g., if you want 3+ pass encoding).

If you want 3-pass or more encoding, keep the box checked and then click on the "Save" function in VirtualDub the same way we did for the FIRST PASS (i.e., above) and then repeat this process until your LAST pass.

If you want this to be the LAST pass (and in this example, it will as we are only doing 2-pass encoding), then uncheck the box.

Again, click okay and we set VirtualDub to "Save":

File --> Save as AVI Set your file name --> check "Don't run this job now"

We can set the same filename as last time.

Now, everything is set and all we need to do now is go to VirtualDub's "job control":

File --> Job control Check that both (or more if 3+ passes) jobs are there --> if everything okay, click Start

And if everything goes well, once both passes are finished, you're left with a nice new DivX AVI file that you've encoded using multipass encoding settings!